This invention relates to the art of making bags and bag making material equipped with reclosable extruded plastic zippers, that is, fasteners which have resiliently flexible releaseably interlockable profiles for extending across the tops of reclosable bags.
As heretofore constructed, bags equipped with extruded zippers have generally been provided with separately formed zipper strips extending across the respective tops of bag walls and having the opposite ends of the separate zipper strips secured together as by heat sealing. This has required producing and handling two separate zipper strips in the bag making process where the strips are separably formed and attached to the bag body sheet or web material. On the other hand, where profiles are integrally extruded with the film, it has been required to extrude separate complementary profile portions of the zipper on separate panels or panel portions of a bag making film.
In recent developments in this art, as covered in copending patents, all assigned to the same assignee as the present application, it has been proposed to provide zippers formed from extruded profiled continuous strips folded upon themselves so that the profiles on the folded strip portions interlock to provide reclosabIe zippers for the bags.
Attention is directed to U.S. Pat. No. 4,666,536 dated May 19, 1987, wherein opposite ends of the zipper strips are heat sealed to the bag wall film, and there is also disclosure of providing a tack or seal at fold in the zipper where the zipper fold is located at a fold in the bag film. Such tacking or sealing of the zipper strip ends or folds facilitates registration of the zipper profiles for closing the zipper
In U.S. Pat. Nos. 4,617,683 dated Oct. 14, 1986 and 4,655,862 dated Apr. 7, 1987, is disclosed that the folding of the zipper strips on themselves can be facilitated by notching the profiles at the folds.
All three of the identified patents disclose applying the zipper strips across the formation axis of the plastic bag forming sheet or film material which provides definite advantages in converting continuous ribbon film into bags, especially in the type of bag filling machines commonly referred to as form, fill and seal machines, such as exemplified in U.S. Pat. No. 4,617,683.
A problem that must be addressed in bags according to the indicated construction resides in avoiding inadvertent opening of the bags due to internal pressures after the bags have been filled.